Circuit arrangements including charge storage tubes



July 28, 1964 n. s. HOBBS 3,142,839

CIRCUIT ARRANGEMENTS INCLUDING CHARGE STORAGE TUBES Filed Jan. 23, 1959 2 Sheets-Sheet 1 IO LSIOIIAL smwomm' OBJECT Ill lllnll lllllll I 3 RS 2 08 m T B m. M 0 8 n a W H T m I a I I N u z m3 f 7 u D m l L j M F L m g/ V N E W. Y 0 A I B R M T E O v V M 1 .HER .r I AME 3 7 UN J I M 3 ll 1 L III'IIIIII M II II We 4 I F. I ANMS E 2 TWW W M EM N I 1 A U T L60 A 7 TR V R c WU c D5 1 S I n s I r w. n m w v 4 .l m N |Hw n. m 0 I ll I l l I l I I l |l.l.||| w F EY- L I LII l l l l I l l l I II a m N G A T .m on .Il SR .Wfi F SC uv July 28, 1964 D. s. HOBBS 3,142,839

CIRCUIT ARRANGEMENTS INCLUDING CHARGE STORAGE l'UBES Filed Jan. 23, 1959 2 Sheets-Sheet 2 STORAGE TUBE lo e 7 DEFLEOTION 3 sIcNAI PULSE A SOURCE SEPARATOR I sIcIIAI.

IIIPIIT -40 RADIAL SCANNING SIGNAL GENERATOR DISPLAY Tues 5'l SI I l I FRAME I FRAME z FRAME 3 FRAME 4 l a VA I 1| .I I I L L srmc t qav I I I OBJ IL I HIL nflIL I I- I l I i I I I I l l I I V I l C l l i T I I I I I I I l l l I I I l I i I I I I V0 I H M I 41m I I i I I I l z I I I I VE I I I l I i I I I I I l l l I INVENTOR.

F G- 4- v DONALD s. HOB

AGENT Unite rates atent Filed Fan. 23, 1959, Ser. No. 783,604 Ciainls priority, appiieation Great Britain Jan. 31, 1958 7 Ciairns. (Ci. 343- 117) This invention relates to circuit arrangements including charge storage tubes. v

Charge storage tubes have an application in radar systems where it is an advantage to eliminate from the display echoes of a permanent nature, so that echoes from moving objects may be more clearly observed. The storage tube can act as a means of delaying the signal received during one radar scan so that it may be compared with that received during the next scan.

In such a system it is possible to employ two charge storage tubes and to write during a scanning period incoming signal information on one tube and read off from the other information Written during the preceding frame. The read-01f information is then compared with the incoming information and the difference signal supplied to the display device. Such an arrangement, however, has the disadvantage that two charge storage tubes with associated switching apparatus are required.

In the United States Patent No. 2,986,673 there is described a circuit arrangement including a charge storage tube having an electron gun comprising a cathode electrode for producing one electron beam, an anode elec trode and a target having a storage surface, said target being provided with a backing of an electrically conductive material constituting a signal plate, scanning means for effecting similar repetitive scans of the beam over a path on the storage surface, signal input means for applying to the cathode during scans input signals to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first crossover potential of the material of the target thereby permitting negative charge to be deposited on the storage surface in accordance with the input signals, and an output circuit connected to the signal plate for deriving simultaneously with the deposition of negative charge on the storage surface output signal information corresponding to the deposition of negative charge. The first cross-over potential of the material of the target is defined as the lower of the two values of electron energies expressed in volts at which the secondary emission coefficient of the material is unity. In the operation of such a circuit arrangement, output signal information can be derived simultaneously with the application to the tube of the input information. The output information obtained during the scan of any element will correspond to the negative charge deposited on that element and this in turn will depend on the amplitude of the input signal and the magnitude of the negative charge (if any) already deposited on that element; thus the output information will be a diiference signal, namely the difference or a function of the difference between the input signal and the signal corresponding to the amount of charge, if any, present on the storage element being scanned.

There is also described a circuit arrangement comprising a source of input signals derived by similar repetitive scans of a field eifected in equal or substantially equal intervals of time, a charge storage tube having an electron gun comprising a cathode electrode for producing one electron beam, an anode electrode and a target having a storage surface, said target being provided with a backin of an electrically conductive material constituting a signal plate, scanning means for effecting similar repetitive scans of the beam over a path of the storage surface in periods equal or substantially equal to the said time intervals, input means for applying to the cathode during scans said input signals so as to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first cross-over potential of the material of the target thereby permitting negative charge to be deposited on the storage surface in accordance with the input signals, whereby in an initial scan the electron beam deposits on the storage surface negative electric charge in accordance with all of the input signals and in subsequent scans deposition of negative charge at any given storage element is prevented or reduced by the presence at the element of any previously deposited negative charge, and an output circuit connected to the signal plate for deriving simultaneously with the deposition of negative charge on the storage surface output signal information corresponding to the deposition of negative charge.

The source of signals may be provided by a radar receiver circuit adapted to produce signals corresponding to echoes from both stationary and moving bodies. Thus in a first scan of the storage surface a pattern of negative charge will be deposited corresponding to the stationary and moving bodies. Providing the beam current during the first scan is adequate to stabilise all storage elements at the corresponding cathode potential, then during subsequent scans deposition of charge due to the signal from a stationary body Will be prevented (assuming in any scan the corresponding incoming signal is not greater in amplitude than that in the first scan) if the negative charge deposited in the initial scan does not leak away. This will be the case with a target of an insulating material when the cathode potential is constant in the absence of input signals.

Thus when the storage tube output signals are fed to a cathode ray display device in which scanning of the luminescent screen is effected in the same time as the scanning of the storage surface of the storage tube, after the first scan stationary bodies will not cause the screen to luminesce. However, in time the whole of the storage tube target will become insensitive because the negative charge deposited thereon due to signals from moving bodies may prevent deposition of further negative charge in accordance with signals from new moving bodies. To overcome this difficulty it is necessary to restore the storage surface by reducing the potential difference between the charged and uncharged storage elements to zero.

For a target of an insulating material this restoration is described in the aforementioned US. Patent No. 2,986,673 as taking place periodically by depositing positive charge after a number of scans or continuously by applying a negative saw-tooth voltage to the cathode during scans. As is described in the United States Patent No. 2,986,673, when the latter method is employed it will be necessary to restabilise periodically the whole target by depositing positive charge on it. In the restabilisation scan of the latter method and in the restoration scan of the former method of target restoration no output information will be obtained and it may be a disadvantage to have periodically a scan in which no output information is obtained.

It is an object of the present invention to provide a circuit arrangement which overcomes this possible dis advantage.

According to one aspect of the present invention there is provided a circuit arrangement including a charge storage tube having an electron gun including a cathode electrode for producing one electron beam, and a target having a storage surface, said target being provided with a backing of an electrically conductive material constituting a signal plate, scanning means for effecting similar repetitive scans of the beam over a path on the storage surface, which scanning path consists of a raster of parallel lines, signal input means for applying to the cathode during scans of said path input signals to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first crossover potential of the material of the target thereby permitting negative charge to be deposited on the storage surface, means for reducing negatively the cathode potential during the line fly-back time intervals in such manner that the electron beam during such time intervals is defocussed and the potential difference between the cathode and the elements of the storage surface being swept in such intervals is increased to a value greater than the first cross-over potential so that the secondary emission coefficient of the material of the target is greater than unity whereby positive charge is deposited substantially uniformly over the storage surface in the time between successive scans by said scanning means of a storage element of said path, and an output circuit connected to the signal plate for deriving, during the scans of said path, output signal information corresponding to deposition of negative charge.

According to a second aspect of the invention there is provided a circuit arrangement including a source of input signals derived by similar repetitive scans of a field effected in equal or substantially equal intervals of time, a charge storage tube having an electron gun including a cathode electrode for producing one electron beam, and a target having a storage surface, said target being provided with a backing of an electrically conductive material constituting a signal plate, scanning means for effecting similar repetitive scans of the beam over a path on the storage surface in periods equal or substantially equal to the said time intervals, which scanning path consists of a raster of parallel lines, signal input means for applying to the cathode during scans of said path the input signals to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first cross-over potential of the material of the target thereby permitting negative charge to be deposited on the storage surface in accordance with the input signals, means for reducing the cathode potential during the line fly-back time intervals in such manner that the electron beam during such fly-back time intervals if defocussed and the potential difference between the cathode and the elements of the storage surface being swept in such fiy-back time intervals is increased to a value greater than the first cross-over potential so that the secondary emission coefiicient of the material of the target is greater than unity whereby positive charge is deposited substantially uniformly over the storage, surface in the time between successive scans by said scanning means of a storage element of said path, and anoutput circuit connected to the signal plate for deriving, during the scans of said path, output signal information corresponding to deposition of negative charge.

The source of input signals may be a radar receiver adapted to producesignals corresponding to echoes from both stationary and moving objects. In such cases the circuit arrangement may include a plan-position indicator cathode ray display tube havinga luminescent screen, scanning means for scanning radial linear paths on the display tube screen in synchronisrnwith the scanning of the lines on the storage surface of the storage tube, andmeans for connecting the storage tube output circuit to the display tube to cause the screen to luminesce in accordance with signals corresponding to the instantaneous" positions of moving objects. The output circuit may be adapted to produce, together with signals corresponding to the instantaneous position of a moving object, signals of opposite polarity corresponding to a previous position or to a number of previous positions of the moving object, in which case the output circuit may include means for reversing the polarity of the latter signals, and means for applying both signals to the same electrode of the display tube, the signals corresponding to previous positions effectively increasing the persistence of the luminescence screen to display the track of the moving object. Preferably the electron beam current during the fly-back time intervals has a value such that at any given time several scans of the target are required before all the elements charged negatively at that time by reason of moving objects are raised to the potential of the cathode whereby signals corresponding to the positions of moving objects at said given time may be produced in the output circuit for several subsequent scans of the storage surface.

A general description of the eflfect of electron bombardment of an insulated target element and how the ratio of the primary current varies with the energy of the primary. electrons has been fully described in the aforementioned. patent and need not be repeated here.

Embodiments of the present invention will now be described, as employed in a radar system, with reference tothe drawings in which:

FIGURE 1 illustrates diagrammatically a storage tube with typical electrode potentials,

FIGURE 2 shows various Voltage waveforms associated with the operation of the storage tube of FIGURE 1,

FIGURE 2 illustrates schematically a circuit arrangement as shown in FIGURE 1 employed with a cathode ray display tube and with means for displaying signals indicating previous positions of a moving object, and

FIGURE 4 shows the voltage waveforms at various points in the circuit arrangement of FIGURE 3.

The storage tube in FIGURE 1 comprises a cathode 1, a control grid electrode 2, and a combined final and collector anode 3. The cathode, control grid and final anode constitute the electron gun of the tube. The anode electrode 3 extends to adjacent the storage surface of an insulating target 4, terminating in a collector mesh 5. Examples of suitable materials for the target are mica, magnesium oxide, calcium fluoride, magnesium fluoride and oxides of silicon. The target has a con ductive backing 6 constituting a signal plate. Input signals from a radar receiver circuit 40 and derived by similar repetitive scans by a rotating radar antenna of a field effected in equal or substantially equal intervals of time are developed across resistor 8 and fed to the cathode via capacitor 7, output signals being developed across resistor 9 of the output circuit and obtained via capacitor 10. The output signals are fed to a radar display device (not shown). Typical electrode potentials are shown in FIGURE 1.

The storage surface is scanned by the electron beam from the electron gun of the tube by means of deflection coils 41 in a rectangular raster of parallel lines, i.e. the storage surface is scanned in both line and frame directions. For this purpose, a conventional source 42 of deflection signals may be provided connected to the deflection coils 41. The deflection signal source 42 is also connected to apply deflection signals to a negative pulse generator 43, which generates a negative pulse during each fiyback period of the line deflection signals. These negative pulses are applied, for example, by way of capacitor 7 to the cathode 1, for a purpose that will be explained in more detail in the following paragraphs. The negative pulse generator may comprise, for example, a difierentiating network such as shown in Radar Electronic Fundamentals, NAVSHIPS 900,016, June 1944, at page 287. Regarding the nature of the scan in the radar display device, it is only necessary that the frame scan times be the same in both the storage tube and display tube and that all the lines in the scan of the screen of the display tube be resolved on the storage tube target. A P.P.I. (Plan Position Indicator) display may be used,

for example, in the display device, the radial scanning in the display tube and the raster scan of the storage tube being effected in periods equal to the time intervals for the scans by the radar antenna. Furthermore, the scanning of the radial paths in the luminescent screen of the display tube must be effected in synchronism with the scanning of the lines of the raster on the storage surface of the storage tube target.

However, to simplify the explanation of the operation of the storage tube, the case of a single line repetitively scanned will first be described, the line fiy-back path in this case coinciding with the line scanning path.

It will now be assumed that the radar receiver is receiving echoes from both a stationary and a moving object and that the echoes received from the objects and in particular the stationary object do not vary in amplitude from scan to scan. The voltage applied to the cathode 1 in the absence of input signals is shown in FIGURE 2(a) while FIGURE 2(1)) shows the complete waveform when negative signals 11 and 12 corresponding to received echoes are also applied to the cathode, reference 11 indicating the signal due to a stationary object and reference 12 indicating the signal due to a moving object. Before the first scan it is assumed that the whole target surface has been stabilised at cathode potential which in this case is zero. The sequence of operations is as follows:

1 st Scan The signals 11 and 12 are of a few volts amplitude being less than the first cross-over potential of the material of the target (FIGURE 2b). Providing the beam current is adequate, then the storage element scanned while a signal is applied to the cathode will be stabilised at the cathode potential as shown in FIGURE 2c, this figure illustrating the storage surface potential after the respective scans and shows elements 13 and 14 of the storage surface of the target stabilised at potentials corresponding to the signals 11 and 12, respectively. During the first scan both the stationary and moving bodies will give rise to negative signals 15 and 16, respectively, at the signal output corresponding to the deposition of negative charge on the target (FIGURE 2d) 1st Fly-Back At the end of the first scan of the line and during the line fly-back time interval the potential of the cathode is reduced by applying thereto a negative pulse 17 from generator 43 of such amplitude that the potential difference between all storage elements and the cathode is greater than the first cross-over potential (but less than the second cross-over potential) of the material of the target (see FIGURE 21)) so that during the fly-back sweep positive charge is deposited substantially uniformly over the scanned path of the storage surface, the amount of positive charge deposited being dependent mainly on the beam current during fly-back and the line fiy-back speed. During the line fly-back therefore, all elements of the scanned path will be raised in potential positively by substantially the same amount.

2nd Scan During the next scan, the scanned storage surface will be restabilised at the cathode potential. Hence an amount of negative charge equal to the amount of positive charge deposited during fly-back will be deposited during the second scan on all elements except those corresponding to the previous and new positions of the moving object. In particular the amount of charge deposited on the element corresponding to the stationary object will be substantially the same as that deposited on all the other elements (with the exceptions previously referred to), so that a steady direct current will flow through resistor 9, and capacitor 16 blocks the flow of direct current to the output circuit. Therefore during the second scan no output will be obtained due to the application of the input signal 11' to the cathode and corresponding to the second echo from the stationary object.

Considering now the scanning of the element negatively charged in the first scan due to the previous position of the moving object, the potential of this element is increased positively due to the positive charge deposited during the fly-back and is indicated at 18 but it is still more negative than the unmodulated cathode potential. Hence, during the second scan no electrons will reach this element and consequently a discontinuity will occur in the direct current which was provided when the other objects were scanned, so that a positive pulse 19 will therefore appear in the signal output corresponding in amplitude to the amount of charge deposited during the line fly-back.

The new position of the moving object will give rise to a received signal 12 and the storage element scanned will be stabilised at the corresponding cathode potential as indicated at M, a negative signal 16' being produced at the storage tube output as before.

2nd F ly-Back During the second fly-back, a negative pulse 17' is applied as before and substantially the same amount of positive charge is depoited on all the elements scanned.

3rd Scan For the reasons explained above, the pulse 11 corresponding to the stationary object will cause the scanned element to be restabilised at the appropriate cathode potential as indicated at 13 but no output pulse will be obtained.

The potential of the element 18 corresponding to the first position of the moving object was again increased positively due to the 2nd fly-back but to a potential still negative with respect to the unmodulated cathode potential as shown at 18 and hence scanning of this element will again give rise to a positive pulse 19' of the same amplitude as that obtained in the 2nd scan. The element I8 is now considered to have a potential less than the increase that all elements experience during line flyback.

In a manner similar to that described for the scanning of element 14 under the heading 2nd Scan, the element 14' corresponding to the second position of the moving object is reduced in potential during the second fiy-back as indicated at 2th and gives rise during the third scan to a positive signal 21 in the output circuit.

The new position of the moving object gives rise to an input signal 12 causing a corresponding negative charging of a storage element as shown at 14 and a negative output signal 16.

3rd Fly-Back As before the cathode potential is reduced by pulse 17 and positive charge deposited substantially uniformly over the whole scanned path.

4th Scan Again, the signal 11" corresponding to the stationary object causes the corresponding scanned element to be restabilised at cathode potential as shown at 13 but no output signal is obtained.

During the third fiy-back scan the potential of the element as represented by 18' is increased positively to a value positive with respect to the unmodulated cathode potential and hence during the fourth scan this element is restored to cathode potential as indicated by reference 18". In view of the fact that some electrons will land on this element to effect this restoration but are fewer in number than reach other elements, for example, the element corresponding to the stationary object, a reduced positive signal 19 will be obtained at the storage tube output.

In a manner similar to that described above, the scanen a es potentials indicated by 20 and 22, respectively, gives rise to positive pulses 21' and 23, respectively, in the signal output circuit. The potential of the element as represented by 20 is now less than that increase that all elements experience during a fly-back sweep.

The new position of the moving object producing signal 12 will cause the corresponding element scanned to be stabilised at cathode potential as indicated at 14" and produce a negative output signal 16.

In the subsequent scans and fly-back sweeps similar events take place. As will be apparent from the above detailed account, the signal output in any scan will be a negative signal indicating the instantaneous position of the moving object and three positive signals indicating the three previous positions of the moving object. In particular it should be noted that after the initial scan, no output for stationary objects is obtained and furthermore that after an element has been charged by the moving object the element is restored to the unmodulated cathode potential during the third subsequent scan of that element.

Of course, the number of scans required for restoration of an element, in which scans positive signals are obtained from the scanning of that element, apart from depending on the beam current during fly-back and the line fly-back speed, will also depend on the extent to which that element is initially negatively charged. Merely for the purposes of the explanation of the invention these factors have been taken to result in positive signals being produced in three scans following that in which an element is first charged negatively by the moving body. Clearly, with a sufiiciently large beam current during fly-back all elements charged in any scan by signals due to moving bodies could be restored to cathode potential during the next scan, but in practice it may be desirable to employ several scans, for example five or six, to restore such a charged element and thereby obtain for each of these subsequent scans a positive signal. These positive signals can be applied, as will be described later, to the display tube to effectively increase the persistence of the screen of the tube and thereby give better indication of the track of the moving object.

The time for total restoration of a storage element stabilised at a negative potential by a signal received from a moving object can be varied by adjusting the beam current during the line fly-back by, for example, suitably pulsing the grid in addition to the cathode.

The restoration process described above is not affected if the scan of the storage surface is, in accordance with the invention, a raster of parallel lines. Although in this case the path of the beam during fly-back would not normally coincide with the path of the beam in the writing scan, the change in cathode potential will cause considerable defocussing of the beam, and, providing the line fiy-back paths are distributed in equal or substantially equal density over the whole storage surface, each storage element will be charged positive by substantially the same amount within the time interval between successive scans of an element. The amount the elements are charged will depend on the beam current during fly-back and the line fiy-back speed. If the potentials of the electrodes other than the cathode remain unchanged during the fly-back periods then the amount of defocussing of the electron beam during fly-back will depend on the potential of the cathode during such periods. The defocussed beam may overlap two or more writing paths but this will not matter and it is only necessary that the same or substantially the same amount of positive charge be deposited on each element in the time between consecutive scan of that element. Under certain conditions it may be arranged that each fly-back period sweeps fly-back sweep to the the defocussed beam during the whole target surface.

The positive signals obtained at the signal output can, if desired, be prevented from reaching the display, and this can be done e.g. by clipping of the output signals.

7 current has not such a 8 In such a case moving echoes will appear without tails to indicate their direction of motion. In an alternative and preferred application, in order to provide such tails the positive signals can be separated, inverted and then fed to the display system with the negative echo signals as will now be described with reference to FIGURES 3 and 4.

As in FIGURE 1, input signals are applied via capacitor 7 and developed across resistor 8. The input signals applied during each of the first four complete frame scans of the target of the storage tube indicated at 24 are shown by the waveform V of FIGURE 4. In. accordance with the charge deposited on the storage target, current will flow through resistor 9 in the output circuit which is capacitively coupled by means of capacitor 10 to a pulse separator circuit 25. The waveform of the input signals to circuit 25 is shown by curve V of FIGURE 4. The circuit 25 separates the negative signals from the positive signals and the waveforms of the two outputs at C and D are shown in FIGURE 4. The positive signals are fed to a pulse inverter circuit 26 and the inverted pulses together with the negative pulses from the separator circuit 25 are applied to an adding circuit 27, the output of which is indicated by waveform V of FIGURE 4. The waveform V is applied to the cathode 28 of a P.P.I. display tube 29 and, as has been described earlier, the inverted pulses effectively increase the persistence of the luminescent screen of the tube 29 enabling the track of the moving object to be readily observed.

The same effect can, of course, be obtained by omitting the inverter circuit 26 and applying the positive signals (waveform V to the control grid electrode 30 of the display tube 29. The adding circuit would also be omitted in this case and the negative signals (waveform V from circuit 25 applied directly to the cathode 28.

If it is not desired to display the positive signals the capacitor 10 and the circuits 25, 26 and 2.7 can. be omitted and the output signal developed across resistor 9 can be applied through a DC. amplifier to the cathode 28 of display tube 29 with an appropriate bias voltage applied to the grid 30 so that only the negative signals cause luminescence of the screen of the display tube.

In the system of FIG. 3, the P.P.I. presentation on display. tube 29 may be obtained by means of deflection coils 50, with deflection signals being applied to the coils 50 from a radial scanning signal generator 51. The necessary synchronism between the scanning systems of tube 29 and storage tube 24 may be provided by conventional means, such as by providing an interconnection between the source 42 and generator 51.

In the description given above it has been assumed that the beam current is adequate to stabilise the target at the instantaneous cathode potential in one scan. If the beam sufiicient value the result will be that output signals will be obtained corresponding to stationary bodies for the number of scans required for the corresponding target elements to be stabilised.

What is claimed is:

1. A circuit arrangement including a charge storage tube having an electron gun including a cathode electrode for producing one electron beam, and a target having a storage surface, said target being provided with a backing of an electrically conductive material constituting a signal plate; scanning means for effecting similar repetitive scans of the beam over a path on the storage surface, which scanning path consists of a raster of parallel lines; signal input means for applying to the cathode during scans of said path input signals to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first cross-over potential of the material of the target thereby permitting negative charge to be deposited on the storage surface; means for reducing the cathode potential with respect to the target potential during the line fiy-back time intervals in such manner that the electron beam during such time intervals is defocussed and the potential difiference between the cathode and the elements of the storage surface being swept in such intervals is increased to a value greater than the first cross-over potential so that the secondary emission coeificient of the material of the target is greater than unity whereby positive charge is deposited substantially uniformly over the storage surface in the time between successive scans by said scanning means of a storage element of said path; and an output circuit connected to the signal plate for deriving, during the scans of said path, output signal information corresponding to deposition of negative charge.

2. A circuit arrangement including a source of input signals derived by similar repetitive scans of a field effected in equal or substantially equal intervals of time; a charge storage tube having an electron gun including a cathode electrode for producing one electron beam, and a target having a storage surface, said target being provided with a backing of an electrically conductive material constituting a signal plate; scanning means for effecting similar repetitive scans of the beam over a path on the storage surface in periods equal or substantially equal to the said time intervals, which scanning path consists of a raster of parallel lines; signal input means for applying to the cathode during scans of said path the input signals to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first cross-over potential of the material of the target thereby permitting negative charge to be deposited on the storage surface in accordance with the input signals; means for reducing the cathode potential during the line fly-back time intervals in such manner that the electron beam during such fly-back time intervals is defocussed and the potential difference between the cathode and the elements of the storage surface being swept in such fly-back time intervals is increased to a value greater than the first crossover potential so that the secondary emission coeflicient of the material of the target is greater than unity whereby positive charge is deposited substantially uniformly over the storage surface in the time between successive scans by said scanning means of a storage element of said path; and an output circuit connected to the signal plate for deriving, during the scans of said path, output signal information corresponding to deposition of negative charge.

3. A circuit arrangement as claimed in claim 2, Wherein the source of input signals is a radar receiver adapted to produce signals corresponding to echoes from both stationary and moving objects.

4. A circuit arrangement including a radar receiver constituting a source of input signals corresponding to echoes from both stationary and moving objects and derived by similar repetitive scans of a field effected in equal or substantially equal intervals of time; a charge storage tube having an electron gun including a cathode electrode for producing one electron beam, and a target having a storage surface, said target being provided with a backing of an electrically conductive material constituting a signal plate; scanning means for effecting similar repetitive scans of the beam over a path on the storage surface in periods equal or substantially equal to the said time intervals, which scanning path consists of a raster of parallel lines; signal input means for applying to the cathode during scans of said path the input signals to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first cross-over potential of the material of the target thereby permitting negative charge to be deposited on the storage surface in accordance with the input signals; means for reducing the cathode potential during the line fly-back time intervals in such manner that the electron beam during such fiy-back time intervals is defocussed and the potential difference between the cathode and the elements of the storage surface being swept in such flyback time intervals is increased to a value greater than the first cross-over potential so that the secondary emission coeflicient of the material of the target is greater than unity whereby positive charge is deposited substantially uniformly over the storage surface in the time between successive scans by said scanning means of a storage element of said path; an output circuit connected to the signal plate for deriving, during the scans of said path, output signal information corresponding to deposition of negative charge; a plan-position indicator cathode ray dis play tube having a luminescent screen; scanning means for scanning radial linear paths on the display tube screen in synchronism With the scanning of the lines on the storage surface of the storage tube; and means for connecting the storage tube output circuit to the display tube to cause the screen to luminesce in accordance with signals corresponding to the instantaneous positions of moving objects.

5. A circuit arrangement as claimed in claim 4, where in the output circuit is adapted to produce, together with signals corresponding to the instantaneous position of a moving object, signals of opposite polarity corresponding to a previous position or to a number of previous positions of the moving object.

6. A circuit arrangement as claimed in claim 4, wherein the output circuit is adapted to produce, together with signals corresponding to the instantaneous position of a moving object, signals of opposite polarity corresponding to a previous position or to a number of previous positions of the moving object, the output circuit including means for reversing the polarity of the latter signals, and means for applying both signals to the same electrode of the display tube, the signals corresponding to previous positions effectively increasing the persistence of the luminescent screen to display the track of the moving object.

7. A circuit arrangement including a radar receiver constituting a source of input signals corresponding to echoes from both stationary and moving objects and derived by similar repetitive scans of a field effected in equal or substantially equal intervals of time; a charge storage tube having an electron gun including a cathode electrode for producing one electron beam, and a target having a storage surface, said target being provided with a backing of an electrically conductive material constituting a signal plate; scanning means for effecting similar repetitive scans of the beam over a path on the storage surface in periods equal or substantially equal to the said time intervals, which scanning path consists of a raster of parallel lines; signal input means for applying to the cathode during scans of said path the input signals to cause negative excursions of the cathode potential while ensuring that the potential difference between the storage element being scanned and the cathode is less than the first cross-over potential of the material of the target thereby permitting negative charge to be deposited on the storage surface in accordance with the input signals; means for reducing the cathode potential during the line fly-back time intervals in such manner that the electron beam during such flyback time intervals is defocussed and the potential difference between the cathode and the elements of the storage surface being swept in such fly-back time intervals is increased to a value greater than the first cross-over potential so that the secondary emission coefiicient of the material of the target is greater than unity whereby positive charge is deposited substantially uniformly over the storage surface in the time between successive scans by said scanning means of a storage element of said path; an output circuit connected to the signal plate for deriving, during the scans of said path, output signal information corresponding to deposition of negative charge; a plan-position indicator cathode ray display tube having a luminescent screen; scanning means for scanning radial linear paths on the display tube screen in synchronism 1 1 with the scanning of the lines on the storage surface of the storage tube; and means for connecting the storage tube output circuit to the display tube to cause the screen to luminesce in accordance with signals corresponding to the instantaneous positions of moving objects; wherein the electron beam current during the fly-back time intervals has a value such that at any given time several scans of the target are required before all the elements charged negatively at that time by reason of moving objects are raised to the potential of the cathode whereby the output circuit is adapted to produce, together with signals corresponding to the instantaneous position of moving objects, signals of opposite polarity corresponding to the Cil- . t 12 7 positions of moving objects at said given time for several subsequent scans of the storage surface; the output circuit including means for reversing the polarity of the latter signals, and means for applying both signals to the same electrode of the display tube, the signals corresponding to previous positions effectively increasing the persistence of the luminescent screen to display the track of the moving object.

References Cited in the file of this patent UNITED STATES PATENTS 2,547,638 Gardner Apr. 3, 1951 2,718,609 Covely Sept. 20, 1955 

4. A CIRCUIT ARRANGEMENT INCLUDING A RADAR RECEIVER CONSTITUTING A SOURCE OF INPUT SIGNALS CORRESPONDING TO ECHOES FROM BOTH STATIONARY AND MOVING OBJECTS AND DERIVED BY SIMILAR REPETITIVE SCANS OF A FIELD EFFECTED IN EQUAL OR SUBSTANTIALLY EQUAL INTERVALS OF TIME; A CHARGE STORAGE TUBE HAVING AN ELECTRON GUN INCLUDING A CATHODE ELECTRODE FOR PRODUCING ONE ELECTRON BEAM, AND A TARGET HAVING A STORAGE SURFACE, SAID TARGET BEING PROVIDED WITH A BACKING OF AN ELECTRICALLY CONDUCTIVE MATERIAL CONSTITUTING A SIGNAL PLATE; SCANNING MEANS FOR EFFECTING SIMILAR REPETITIVE SCANS OF THE BEAM OVER A PATH ON THE STORAGE SURFACE IN PERIODS EQUAL OR SUBSTANTIALLY EQUAL TO THE SAID TIME INTERVALS, WHICH SCANNING PATH CONSISTS OF A RASTER OF PARALLEL LINES; SIGNAL INPUT MEANS FOR APPLYING TO THE CATHODE DURING SCANS OF SAID PATH THE INPUT SIGNALS TO CAUSE NEGATIVE EXCURSIONS OF THE CATHODE POTENTIAL WHILE ENSURING THAT THE POTENTIAL DIFFERENCE BETWEEN THE STORAGE ELEMENT BEING SCANNED AND THE CATHODE IS LESS THAN THE FIRST CROSS-OVER POTENTIAL OF THE MATERIAL OF THE TARGET THEREBY PERMITTING NEGATIVE CHARGE TO BE DEPOSITED ON THE STORAGE SURFACE IN ACCORDANCE WITH THE INPUT SIGNALS; MEANS FOR REDUCING THE CATHODE POTENTIAL DURING THE LINE FLY-BACK TIME INTERVALS IN SUCH MANNER THAT THE ELECTRON BEAM DURING SUCH FLY-BACK TIME INTERVALS IS DEFOCUSSED AND THE POTENTIAL DIFFERENCE BETWEEN THE CATHODE AND THE ELEMENTS OF THE STORAGE SURFACE BEING SWEPT IN SUCH FLYBACK TIME INTERVALS IS INCREASED TO A VALUE GREATER THAN THE FIRST CROSS-OVER POTENTIAL SO THAT THE SECONDARY EMISSION COEFFICIENT OF THE MATERIAL OF THE TARGET IS GREATER THAN UNITY WHEREBY POSITIVE CHARGE IS DEPOSITED SUBSTANTIALLY UNIFORMLY OVER THE STORAGE SURFACE IN THE TIME BETWEEN SUCCESSIVE SCANS BY SAID SCANNING MEANS OF A STORAGE ELEMENT OF SAID PATH; AN OUTPUT CIRCUIT CONNECTED TO THE SIGNAL PLATE FOR DERIVING, DURING THE SCANS OF SAID PATH, OUTPUT SIGNAL INFORMATION CORRESPONDING TO DEPOSITION OF NEGATIVE CHARGE; A PLAN-POSITION INDICATOR CATHODE RAY DISPLAY TUBE HAVING A LUMINESCENT SCREEN; SCANNING MEANS FOR SCANNING RADIAL LINEAR PATHS ON THE DISPLAY TUBE SCREEN IN SYNCHRONISM WITH THE SCANNING OF THE LINES ON THE STORAGE SURFACE OF THE STORAGE TUBE; AND MEANS FOR CONNECTING THE STORAGE TUBE OUTPUT CIRCUIT TO THE DISPLAY TUBE TO CAUSE THE SCREEN TO LUMINESCE IN ACCORDANCE WITH SIGNALS CORRESPONDING TO THE INSTANTANEOUS POSITION OF MOVING OBJECTS. 